This application claims priority to China Patent Application No. 201210358060.1 filed on Sep. 24, 2012 entitled, OPTICAL COMPENSATION FILMS AND METHOD FOR REDUCING DARK-STATE LIGHT LEAKAGE OF VERTICAL ALIGNMENT LIQUID CRYSTAL DISPLAY, all of the disclosures of which are incorporated herein by reference in their entirety.
1. Field of the Invention
Embodiments of the present disclosure relate to optical technology, and more particularly to optical compensation films and a method for reducing dark-state light leakage of vertical alignment liquid crystal display.
2. Discussion of the Related Art
As the view angles of the thin film transistor LCD (TFT-LCD) increase, the contrastness and the resolution of the display are decreased for the reason that the birefringence of the liquid crystal changes in accordance with the change of the view angles. By adopting wide view angle compensation films, the dark-state light leakage may be reduced and the brightness of the display may be greatly increased.
Normally, the compensation films amend the phase displacements of the liquid crystal in different view angles so that the birefringence of the liquid crystal is compensated symmetrically. Different compensation films are designed for different display modes of liquid crystal. For example, vertical alignment (VA) display modes are for large size liquid crystal display. Other examples include the N-TAC compensation films of Konica, Zeonor films of OPOTES, F-TAC compensation films of Fujitsu, and X-plate films of Nitto Denko. The conventional single-layer biaxial compensation structure is shown in FIG. 1 and the conventional double-layers biaxial compensation structure is shown in FIG. 2. The single-layer biaxial compensation structure is formed by a Triacetate Cellulose (TAC) film, a Poly Vinyl Alcohol (PVA) film, the TAC compensation film, a Pressure Sensitive Adhesive (PSA) film, a VA cell film, the PSA film, a biaxial film, the PVA film, the TAC compensation film in turn.
Adopting the double-layers biaxial compensation structure decreases the dark-state light leakage to enhance the brightness and the resolution. However, the cost of the double-layers biaxial compensation structure is high. In addition, adopting the single-layer biaxial compensation structure may reduce the cost, but the dark-state light leakage may happen.
FIGS. 3 and 4 are distribution diagrams showing the dark-state light leakage of the conventional single-layer biaxial and double-layers biaxial compensation structure when the light path difference (LCΔND) is equal to 333.6 nm and the pretilt angle is 89 degree.
FIGS. 5 and 6 are simulation diagrams of the contrastness distribution for the conventional single-layer biaxial and double-layers biaxial compensation structures in a wide viewing angle. It can be seen from FIGS. 3 to 6 that the light leakage of the double-layers biaxial compensation structure is much less than that of the single-layer biaxial compensation structure. In addition, the contrastness distribution of the double-layers biaxial compensation structure is also better that that of the single-layer biaxial compensation structure.
Therefore, there is a need to solve the dark-state light leakage using the single-layer biaxial compensation structure.